Secularism is not the absence of religion from public life. It is a family of political arrangements for managing disagreement about ultimate truth. Different societies have answered the same question — what do we do when citizens disagree about what God requires? — in structurally different ways. Understanding those differences is more analytically useful than treating secularism as a single thing.
France bans headscarves in public schools. The United Kingdom has twenty-six Church of England bishops in the House of Lords. The United States forbids an established church but opens its Supreme Court sessions with the phrase ‘God save this honorable court.’ Turkey was constitutionally secularist for decades but the secularism meant state control of religion, not religion’s absence. India is constitutionally secular but its secularism means equal respect for all religions, not their equal exclusion. These are not the same thing. They are different answers to the same question.